Assessment of Neuro-Musculo-Vascular Activity in Hemiplegic Shoulder Pain: A Multimodal Study With HD-sEMG, Ultrasonography, and Laser Speckle Imaging

Hemiplegic shoulder pain (HSP) is a common complication following stroke, significantly affecting upper limb recovery and quality of life. However, the underlying pathophysiological mechanisms of HSP remain poorly understood, which poses a major obstacle to the development of effective therapeutic strategies. This study aims to investigate the underlying mechanism of HSP by evaluating neuro-musculo-vascular activities using high-density surface electromyography (HD-sEMG), musculoskeletal ultrasound, and laser speckle contrast imaging (LSCI). A total of 12 HSP patients and 12 hemiplegic controls without shoulder pain (HNSP) participated in this study. Their neuro-musculo-vascular data in the affected shoulder were collected using a 64-channel HD-sEMG electrode array, a musculoskeletal ultrasonic probe, and a LSCI sensor. Muscle activity was quantified by the root mean square (RMS) of HD-sEMG signals, while neural firing activity was characterized by the discharge rate and coefficient of variation (CoV), decomposed from the HD-sEMG. Meanwhile, structural characteristics were measured by the shoulder subluxation distance (SSD) from ultrasonic image, and blood perfusion was evaluated by perfusion units (PU) from LSCI. Results showed significantly lower RMS and CoV in HSP group versus HNSP group (p<0.05), both strongly correlated with pain intensity (RMS: r=-0.792, ${p}={0}.{002}$ ; CoV: r=-0.698, p= 0.012 ). Pain intensity also linked to greater SSD (p <0.001) but not PU value (p >0.05), while SSD negatively correlated with both RMS and CoV (p <0.05). These findings suggest that HSP is more closely related to neuromuscular control abnormalities and shoulder joint instability than to microcirculatory dysfunction, emphasizing the need for targeted neuromuscular rehabilitation in treating HSP.